4 ms·

Is flying in a thin atmosphere harder? Sure, there is less lift... But there is also less drag. So your rotors can go far faster with the same power input -

Is flying in a thin atmosphere harder? Sure, there is less lift... But there is also less drag. So your rotors can go far faster with the same power input - and, roughly, it looks like the power needed to hover (for a craft of a given mass and size) is actually less on mars due to the lower gravity, despite the rotors moving super fast.

sobellian 3y ago
In the limit of no atmosphere, it's surely impossible. In the case of a thick, incompressible atmosphere (a body of water), even humans can do it.
- Intralexical 3y ago
  "Titan's gravity is 14% of Earth's, and its atmosphere 50% denser. So if you can generate 9% of your Earth body weight in lift, you can fly on Titan." https://xkcd.com/620/ https://xkcd.com/620/
- londons_explore 3y ago
  > even humans can do it. I think this is a misconception. Even in water, you cannot provide lift equal to your bodyweight. It is easier to swim (vs sink) in water because the water gives a large amount of buoyancy. However, in air and on mars, buoyancy is small enough to be negligible.
  - sobellian 3y ago
    It's true that buoyancy helps, but even so swimming clearly provides a greater propulsive force than doing the same motion in air despite the greater drag in water.
malfist 3y ago
Less drag means less lift. Drag is how rotars generate lift
godelski 3y ago
> less lift... But there is also less drag FYI, these two things are __directly__ related. Lift = c0 r v^2 A Drag = c1 r v^2 A => Lift = c0/c1 Drag You should be able to reason this out too. Think about how you generate lift. The blades spinning have to push something, right? What is it pushing? Then think about drag. What is that dragging against? Is it related to the thing you're also pushing against? I think you know the answer.
eastbound 3y ago
According to this ballpark calculation, it would take the same energy for a helicopter to fly on the Everest (with ultrafast rotors, which they don’t have) as in water (ultraslow rotors). Since the lack of helicopters in high mountains (>5000m) is a longstanding issue, it doesn’t look like a good approximation at initial glance.
- robryk 3y ago
  Helicopters on Earth use internal combustion engines (often in particular jet engines) to provide power. Those engines' performance depends on the air pressure (and temperature and humidity).
EB66 3y ago
> Is flying in a thin atmosphere harder? Yep. Setting maths and motors aside... it's why helicopters have service ceilings and why no one has built a helicopter that can fly away into the stratosphere.
- londons_explore 3y ago
  Isn't that just because a helicopter design that can fly in the stratosphere wouldn't be able to fly at sea level? Just like the mars helicopter cannot fly on earth.
jakobson14 3y ago
Drag isn't relevant for a helicopter. Thin air means you have a very hard time just trying to hover in place without moving.

sobellian 3y ago

In the limit of no atmosphere, it's surely impossible. In the case of a thick, incompressible atmosphere (a body of water), even humans can do it.

Intralexical 3y ago
"Titan's gravity is 14% of Earth's, and its atmosphere 50% denser. So if you can generate 9% of your Earth body weight in lift, you can fly on Titan." https://xkcd.com/620/ https://xkcd.com/620/
londons_explore 3y ago
> even humans can do it. I think this is a misconception. Even in water, you cannot provide lift equal to your bodyweight. It is easier to swim (vs sink) in water because the water gives a large amount of buoyancy. However, in air and on mars, buoyancy is small enough to be negligible.
- sobellian 3y ago
  It's true that buoyancy helps, but even so swimming clearly provides a greater propulsive force than doing the same motion in air despite the greater drag in water.

malfist 3y ago

Less drag means less lift. Drag is how rotars generate lift

godelski 3y ago

> less lift... But there is also less drag FYI, these two things are __directly__ related. Lift = c0 r v^2 A Drag = c1 r v^2 A => Lift = c0/c1 Drag You should be able to reason this out too. Think about how you generate lift. The blades spinning have to push something, right? What is it pushing? Then think about drag. What is that dragging against? Is it related to the thing you're also pushing against? I think you know the answer.

eastbound 3y ago

According to this ballpark calculation, it would take the same energy for a helicopter to fly on the Everest (with ultrafast rotors, which they don’t have) as in water (ultraslow rotors). Since the lack of helicopters in high mountains (>5000m) is a longstanding issue, it doesn’t look like a good approximation at initial glance.

robryk 3y ago
Helicopters on Earth use internal combustion engines (often in particular jet engines) to provide power. Those engines' performance depends on the air pressure (and temperature and humidity).

EB66 3y ago

> Is flying in a thin atmosphere harder? Yep. Setting maths and motors aside... it's why helicopters have service ceilings and why no one has built a helicopter that can fly away into the stratosphere.

londons_explore 3y ago
Isn't that just because a helicopter design that can fly in the stratosphere wouldn't be able to fly at sea level? Just like the mars helicopter cannot fly on earth.

jakobson14 3y ago

Drag isn't relevant for a helicopter. Thin air means you have a very hard time just trying to hover in place without moving.